You now master the Explore → Plan → Code → Test workflow. But the quality of results depends enormously on how you formulate your requests. Today, we’ll cover prompt engineering techniques specific to Claude Code.
The Fundamental Principle: Specificity
The difference between a good and bad prompt:
| Bad prompt | Good prompt |
|---|---|
| “Add tests” | “Add unit tests for the calculateDiscount function covering: negative price, discount > 100%, and nominal case” |
| “Fix the bug” | “The bug: TypeError: Cannot read property 'id' of undefined at line 42 of @src/api/users.ts. Fix by adding a null check.” |
| “Improve the code” | “Refactor @src/utils/helpers.ts to extract validation functions into a separate validators.ts module” |
Structure of an Effective Prompt
The CCAR Template
CONTEXT: [Current situation]
CONSTRAINTS: [Limitations to respect]
ACTION: [What you want]
RESULT: [Expected format]
Applied Example
> CONTEXT: I have a React component `UserProfile` that's 300 lines.
It handles display, API calls, and form validation.
CONSTRAINTS:
- Keep compatibility with existing tests
- Don't change public props
- Use existing hooks in @src/hooks/
ACTION: Split this component following the Container/Presenter pattern.
RESULT: Show me the split plan before coding.
Advanced Techniques
1. Provide Examples (Few-shot)
> I want utility functions to follow this pattern:
/**
* Calculates price including tax from price excluding tax
* @param priceExTax - Price excluding tax
* @param vatRate - VAT rate (e.g., 0.20 for 20%)
* @returns Price including tax rounded to 2 decimals
* @throws {InvalidPriceError} If price is negative
*/
export function calculateIncTax(priceExTax: number, vatRate: number): number {
if (priceExTax < 0) throw new InvalidPriceError('Price cannot be negative');
return Math.round((priceExTax * (1 + vatRate)) * 100) / 100;
}
Create a `calculateDiscount` function that follows exactly this pattern.
2. Specify Negative Constraints
What you don’t want is equally important:
> Refactor this code with these constraints:
DO NOT:
- Add new dependencies
- Modify public function signatures
- Change observable behavior
- Use any or as unknown
DO:
- Extract duplicated functions
- Improve typing
- Add early returns
3. Ask for Multiple Options
> Propose 3 different approaches to implement request caching:
1. A simple approach with Map
2. An approach with TTL and invalidation
3. An approach with Redis
For each approach, indicate: complexity, advantages, disadvantages.
4. Use File Context
> By analyzing @src/api/users.ts and @src/api/products.ts,
identify the common pattern and create a generic factory
for CRUD endpoints.
5. Chain Requests
Instead of one big request, chain them:
> Step 1: List performance issues in @src/components/DataTable.tsx
[Claude lists 5 issues]
> Step 2: For issue #2 (unnecessary re-renders), propose a solution
[Claude proposes]
> Step 3: Implement this solution with useMemo
Prompt Patterns for Common Cases
Debugging
> BUG: [Description]
ERROR: [Exact error message]
FILE: @path/to/file.ts:LINE
REPRODUCTION: [Steps to reproduce]
Analyze and propose a fix.
Code Review
> Review @src/features/checkout/payment.ts checking:
1. Security (injection, XSS, validation)
2. Error handling (try/catch, business errors)
3. Performance (N+1, memory)
4. Maintainability (naming, complexity)
Format: list issues by category with severity (critical/medium/low)
Refactoring
> Refactor @src/legacy/oldModule.ts:
OBJECTIVE: Migrate to the new pattern used in @src/modules/newModule.ts
KEEP: Existing tests must pass
REMOVE: Dead code identified by ESLint
ADD: Strict TypeScript types
Documentation
> Generate JSDoc documentation for @src/lib/auth.ts:
- Description of each public function
- @param with types and descriptions
- @returns with type and description
- @throws for possible errors
- @example with a use case
Style: concise, technical, no fluff
Tests
> Generate tests for @src/services/orderService.ts:
FRAMEWORK: Vitest
PATTERN: Arrange-Act-Assert
COVERAGE:
- Nominal case (happy path)
- Error cases (validation, DB, network)
- Edge cases (null, undefined, empty)
MOCKS: Use factories in @tests/factories/
Keywords That Change Everything
For Thinking
| Keyword | Effect |
|---|---|
think |
Basic reflection |
think hard |
Deep reflection |
think harder |
Thorough analysis |
ultrathink |
Maximum reflection |
step by step |
Explicit decomposition |
analyze |
Focus on analysis vs action |
For Format
| Keyword | Effect |
|---|---|
concise |
Short answers |
detailed |
Complete explanations |
list |
Bullet point format |
table |
Markdown table format |
code only |
No explanations, just code |
For Action
| Keyword | Effect |
|---|---|
don't code yet |
Force plan mode |
show before applying |
Preview changes |
one step at a time |
Incremental implementation |
suggest alternatives |
Multiple options |
Common Mistakes to Avoid
1. The Vague Prompt
❌ Bad:
> Improve this code
✅ Good:
> Improve @src/utils/date.ts by:
1. Replacing moment.js with date-fns
2. Adding strict typing
3. Adding tests for timezone edge cases
2. Too Much at Once
❌ Bad:
> Create a complete authentication system with OAuth, 2FA, sessions,
rate limiting, audit logs, and admin dashboard
✅ Good:
> Step 1: Create the database schema for authentication
(users, sessions, oauth_accounts)
3. No Context
❌ Bad:
> Why doesn't this work?
✅ Good:
> This function returns undefined instead of the user object:
@src/api/users.ts:42-55
Expected input: { email: "test@example.com" }
Expected output: { id: 1, email: "test@example.com", name: "Test" }
Actual output: undefined
Here are the logs: !`npm run debug:users 2>&1`
4. Ignoring Project Constraints
❌ Bad:
> Use Redux for state management
✅ Good:
> Using Zustand (already configured in @src/store/),
add a store to manage the shopping cart
Optimized CLAUDE.md Template
Here’s a CLAUDE.md template that drastically improves responses:
# CLAUDE.md
## Project Context
[Application type, tech stack, business constraints]
## Code Conventions
- Naming: [camelCase, PascalCase, etc.]
- Structure: [Feature-based, Layer-based, etc.]
- Patterns: [Hooks, HOC, Render Props, etc.]
## Useful Commands
- `npm run dev`: Development
- `npm run test`: Tests
- `npm run lint`: Linting
- `npm run typecheck`: TypeScript
## Strict Rules
- NEVER modify files in /config/
- NEVER commit .env files
- ALWAYS use strict types (no any)
- ALWAYS add tests for new code
## Tech Stack
- Framework: [Next.js 14, etc.]
- State: [Zustand, etc.]
- DB: [PostgreSQL + Prisma, etc.]
- Tests: [Vitest + Testing Library, etc.]
## Good Code Examples
See @src/features/auth/ for the pattern to follow.
What’s Coming Tomorrow
In Day 5, we’ll dive into context and memory management: how Claude Code remembers your preferences and how to optimize long sessions.
This article is part of the “Master Claude Code in 20 Days” series. Day 3: The Explore → Plan → Code → Test Workflow
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